Android实现快速滚动FastScrollView效果

public class FastScrollView extends ScrollView {
 
    private Rect mBarRect = new Rect();
    private int mScrollExWidth;
    private int mScrollExHeight;
    private boolean mScrollStart;
    private int dx, dy;
    private int mRightPadding;
 
    public FastScrollView(Context context) {
        super(context);
        init();
    }
 
    public FastScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }
 
    public FastScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }
 
    private void init() {
        mScrollExWidth = dip2px(16); //扩展拖动区域宽度，可自行修改
        mScrollExHeight = dip2px(50); //扩展拖动区域高度，可自行修改
    }
 
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        switch (ev.getAction() & ev.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
                //Log.e("fly", "down");
                mScrollStart = false;
                if (canScroll()) {
                    dx = (int) ev.getX();
                    dy = (int) ev.getY();
                    float scrollPos = (float) getHeight() / getChildView().getHeight();
                    int barHeight = (int) (scrollPos * getHeight());
                    //Log.e("fly", scrollPos+", "+ barHeight);
                    mBarRect.left = getWidth() - mRightPadding - getVerticalScrollbarWidth();
                    mBarRect.right = getWidth() - mRightPadding;
                    mBarRect.top = (int) (getScrollY() * scrollPos);
                    mBarRect.bottom = mBarRect.top + barHeight;
                    //Dbg.print(mBarRect.left, mBarRect.right, mBarRect.top, mBarRect.bottom, dx, dy);
                    if (dx >= mBarRect.left - mScrollExWidth
                            && dx < mBarRect.right
                            && dy >= mBarRect.top - mScrollExHeight
                            && dy < mBarRect.bottom + mScrollExHeight) {
                        //Log.e("fly", "mScrollStart");
                        mScrollStart = true;
                    }
                }
                break;
            case MotionEvent.ACTION_MOVE:
                if (mScrollStart) {
                    int offsetY = (int) ev.getY() - dy;
                    //Log.e("fly", "move: " + ev.getY());
                    int top = mBarRect.top + offsetY;
                    float scrollPos = (float) top / getHeight();
                    int scrollY = (int) (scrollPos * getChildView().getHeight());
                    if (scrollY < 0) {
                        scrollY = 0;
                    }
                    if (scrollY > getChildView().getHeight() - getHeight()) {
                        scrollY = getChildView().getHeight() - getHeight();
                    }
                    setScrollY(scrollY);
                    return true;
                }
                break;
        }
        return super.dispatchTouchEvent(ev);
    }
 
    private boolean canScroll() {
        View child = getChildView();
        if (child != null && child.getHeight() > getHeight()) {
            return true;
        } else {
            return false;
        }
    }
 
    private View getChildView() {
        if (getChildCount() > 0) {
            return getChildAt(0);
        } else {
            return null;
        }
    }
 
    private int dip2px(float dpValue) {
        final float scale = getContext().getResources().getDisplayMetrics().density;
        return (int) (dpValue * scale + 0.5f);
    }
 
    /**
     * 这里不用view的paddding，用于预留特殊空隙
     *
     * @param mRightPadding
     */
    public void setRightPadding(int mRightPadding) {
        this.mRightPadding = mRightPadding;
    }
}

<com.zwxuf.apkparserdemo.FastScrollView
	android:id="@+id/mScrollView"
	android:layout_width="0dp"
	android:layout_weight="1"
	android:scrollbarSize="10dp" 
	android:paddingRight="10dp"
	android:scrollbarThumbVertical="@drawable/fast_scroll_thumb_drawable"
	android:layout_height="match_parent">
 
	<HorizontalScrollView
		android:layout_width="match_parent"
		android:layout_height="match_parent" >
 
		<EditText
			android:id="@+id/et_xml"
			android:layout_width="wrap_content"
			android:layout_height="wrap_content"
			android:background="@null"
			android:editable="false"
			android:textColor="#000000"
			android:textSize="10sp"
			android:typeface="monospace"/>
	</HorizontalScrollView>
 
</com.zwxuf.apkparserdemo.FastScrollView>